Which one is better? Coming from someone who doesnt know much about OSM, what I immediately notice is that accoridng to the play store osmand has in-app payments whereas organic maps doesn't.
The answer there likely dives too much into personal preferences to be a "one size fits all" answer.
Both are available on f-droid, so just try both and pick the one you prefer:
Osmand: https://f-droid.org/en/packages/net.osmand.plus/
Organic Maps: https://f-droid.org/en/packages/app.organicmaps/
Organic Maps is a better starting point IMHO.